Some people just like to tinker with things. Amiga users seem more likely than your average computer user. It's a way to learn about computers, how they work, how to make them, how to improve on them, etc. Can you add AGA to your A500, PPC CPUs, built-in flickerfixers, more memory, modern DDR memory, PCI slots, AGP slots, PCI-Express slots, or shove it into a PowerPC system as an addon such as into SAM440's FPGA? Check out
www.opencores.org for more possibilities to add in there... Maybe add an OpenGraphics core as well. Smaller system size could allow something like the C64DTV to happen.
Minimig is the first step in being able to do all kinds of things that can't be done with an A500. It allows a huge number of things to become possible, which are far less convenient to do with an actual A500, if possible at all. It can become more than an A500, in time it can become an A1200, an A4000, an A5000, or who knows what will be imagined into larger capacity/pins FPGAs and different form factors.